1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention relates to papermaker's fabrics, namely the forming, press, dryer fabrics, and through air dryer (TAD) fabrics, also known as paper machine clothing, on which paper is manufactured on a paper machine. Also, the invention may be used as a substrate for a shoe press or transfer or calender belt, any of which can also be used on a paper machine. In addition, the present invention may be applied in other industrial settings where industrial belts are used to dewater a material. Furthermore, the present invention may be used as a belt and/or sleeve used in the production of nonwovens by processes such as airlaid, melt blowing, spunbonding, and hydroentangling.
2. Description of the Prior Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, on a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulose fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speed. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
It should also be appreciated that the vast majority of forming, press and dryer fabrics are, or at least include as a component, a woven fabric in the form of an endless loop having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce forming, press and dryer fabrics to the dimensions required to fit particular positions in the forming, press and dryer sections of the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
Moreover, because the surface of a woven fabric is necessarily uneven to some degree, as knuckles formed where yarns lying in one direction of the fabric wrap around those lying in another direction lie on the surface, it is difficult to produce a paper product entirely free of sheet marking.
The prior art includes several attempts to solve these problems. For example, U.S. Pat. No. 3,323,226 to Beaumont et al. relates to a synthetic dryer belt comprising one or more plies of polyester film. Perforations through the belt are formed by mechanical punching. U.S. Pat. No. 4,495,680 to Beck shows a method and apparatus for forming a base fabric composed solely of warp yarns to be used in making a papermaker's belt. Essentially, the warp yarns are helically wound about two parallel rolls. Subsequently, fibrous batting or other nonwoven material is applied and adhered to the helical array of warp yarns to provide a fillingless papermaker's belt, which is to say that it has no cross-machine direction yarns.
U.S. Pat. No. 4,537,658 to Albert shows a papermaker's fabric made from a plurality of elongated, linked, slotted elements. The elongated elements are linked one to the next either by an integral tongue or through the use of a pintle connecting means which extends from one elongated element to the adjacent element. The elongated elements extend in the cross-machine direction of the disclosed papermaker's fabric, and have flat, parallel top and bottom surfaces.
U.S. Pat. No. 4,541,895 to Albert describes a papermaker's fabric made up of a plurality of nonwoven sheets laminated together to define a fabric or belt. The nonwoven sheets are perforated by laser drilling. Such sheets are composed of unoriented polymer material, and if produced in the fineness needed for papermaking applications, would lack sufficient dimensional stability to operate as endless belts on paper machines.
U.S. Pat. No. 4,842,905 to Stech shows a tessellated papermaker's fabric and elements for making the fabric. The elements are formed so as to have male or projection members which interlock with female or recess members. The papermaker's fabric comprises a plurality of the tessellated elements which have been interconnected to produce a tessellation of a desired length and width.
U.S. Pat. No. 6,290,818 to Romanski shows a shoe press belt wherein the base fabric is made from an endless tube of expanded film which can be perforated.
U.S. Pat. No. 6,630,223 to Hansen shows an industrial belt made from a plurality of spirally wound shaped (non-circular cross-section) monofilaments which are abutted to each other, side to side of adjacent turns and secured to one another by a suitable means.
U.S. Pat. No. 6,989,080 to Hansen shows a nonwoven papermaker's fabric made from a spirally wound MD base layer of raw stock, overlaid with a CD layer of similar or dissimilar raw stock and mated by suitable means.
U.S. Patent Application Publication No. 2007/0134467 A1 to Sayers provides a method comprising the steps of laminating a series of layers of film material and cutting perforations in the laminate to provide a foraminous fabric.
Fabrics in modern papermaking machines may have a width of from 5 feet to over 33 feet, a length of from 40 feet to over 400 feet and weigh from approximately 100 pounds to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. While many fabrics are endless, many of those used today are on-machine-seamable. Installation of the fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
In response to this need to produce fabrics in a variety of lengths and widths more quickly and efficiently, fabrics have been produced in recent years using a spiral winding technique disclosed in commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al. (hereinafter “the '656 patent”), the teachings of which are incorporated herein by reference.
The '656 patent shows a fabric comprising a base fabric having one or more layers of staple fiber material needled thereinto. The base fabric comprises at least one layer composed of a spirally wound strip of woven fabric having a width which is smaller than the width of the base fabric. The base fabric is endless in the longitudinal, or machine, direction. Lengthwise threads of the spirally wound strip make an angle with the longitudinal direction of the fabric. The strip of woven fabric may be flat-woven on a loom which is narrower than those typically used in the production of paper machine clothing.